A fluid machine, in which an expansion mechanism, an electric motor, and an expansion mechanism are coupled by a single rotating shaft, has been known in the conventional technology. In this fluid machine, power is produced by the expansion of fluid introduced into the expansion mechanism. Along with power produced by the electric motor, power produced in the expander is transmitted by the rotating shaft to the compression mechanism. Then, the compression mechanism is driven by both the power transmitted from the expansion mechanism and the power transmitted from the electric motor, and draws in and compresses fluids.
Patent Document I discloses a fluid machine of the type as described above. Referring to FIG. 6 of Patent Document I, there is shown a fluid machine whose vertically long, cylinder-shaped casing houses therein an expansion mechanism, an electric motor, a compression mechanism, and a rotating shaft. In the inside of the casing of the fluid machine, the expansion mechanism, the electric motor, the compression mechanism are arranged in the bottom-to-top order, and they are coupled together by the rotating shaft. In addition, both the expansion mechanism and the compression mechanism are formed by rotary fluid machines.
The fluid machine disclosed in Patent Document I is incorporated into an air conditioner which performs a refrigeration cycle. Low-pressure refrigerant at about 5 degrees Centigrade is drawn into the compression mechanism from the evaporator. The low-pressure refrigerant is compressed and becomes a high-pressure refrigerant of about 90 degrees Centigrade, and the high-pressure refrigerant is expelled from the compression mechanism. The high-pressure refrigerant expelled out of the compression mechanism passes through the internal space of the casing and then through a discharge pipe, and is discharged to the outside of the casing. On the other hand, high-pressure refrigerant at about 30 degrees Centigrade is introduced into the expansion mechanism from the gas cooler. The high-pressure refrigerant is expanded and becomes a low-pressure refrigerant of about 0 degrees Centigrade. The low-pressure refrigerant is delivered to the evaporator.
This type of vertical fluid machine often employs a structure in which lubricating oil accumulated in the bottom of the casing is supplied to the compression mechanism and to the expansion mechanism. When employing such a configuration, an oil supply passage is formed in the rotating shaft. Lubricating oil accumulated in the casing bottom is drawn into the oil supply passageway from the lower end of the rotating shaft by centrifugal pump action et cetera. And, lubricating oil flowing through the oil supply passageway is supplied to the compression and expansion mechanisms and is used to provide lubrication between members.
As described above, fluid compressed in the compression mechanism is often increased in temperature to relatively high-temperature levels. For this reason, in a fluid machine which is constructed such that fluid discharged from the compression mechanism flows through the inside of the casing, the temperature of lubricating oil accumulated in the casing bottom is also increased to relatively high-temperature levels. Accordingly, in fluid machines having such a structure, relatively high-temperature lubricating oil is supplied, through the oil supply passageway, to the compression mechanism and to the expansion mechanism.
Patent Document I: JP 2003-172244A